In a driver device like an IC chip for driving equipment such as an inkjet head, various electronic components are arranged at a high density, and therefore an unintended transistor (parasitic transistor) is sometimes formed between a plurality of components in the driver device. When such a parasitic transistor is formed, an overcurrent flows into the driver device due to the amplification function of the parasitic transistor (latch-up), and the driver device is overheating and, in the worst case, may start on fire.
In order to prevent such driver devices from overheating and staring on fire, some driver device includes therein a circuit (thermal shutdown circuit) for stopping the driver device when the temperature of the driver device becomes higher than a predetermined temperature. For example, in a power supply IC (driver device) disclosed in Japanese Patent Application Laid-Open No. 2005-38921, an Nch MOS transistor is connected to a thermal shutdown circuit composed of an NPN bipolar transistor, and a leakage current in the Nch MOS transistor increases with a rise in the temperature of the power supply IC. When the leakage current of the Nch MOS transistor equals or exceeds 1 μA, the thermal shutdown circuit is activated and the operation of the power supply IC is stopped.